1. Field of the Invention
This disclosure relates to Polycrystalline Diamond Compacts (PDC's) and Polycrystalline Diamond inserts, and in particular, relates to a method of forming such boron-doped PDC's at greatly reduced temperatures.
2. Description of the Related Art
High toughness is a desired property in a single crystal diamond and in polycrystalline diamond compacts (PDC's) for micromachining and rock drilling. Efforts have been made to improve chemical vapor deposition (CVD) single crystal diamond by boron doping its surface. The doping is via the vapor phase of boron in a reactor at temperatures in the 700-1100° C. range as disclosed in U.S. Pat. Nos. 5,981,057, 7,160,617, and 7,201,886. U.S. Pat. No. 5,981,057 was directed to a CVD diamond layer containing at least 0.05% of boron for abrasive resistant tools. U.S. Pat. No. 7,160,617 related to a layer of single crystal boron-doped diamond having a uniform concentration of boron. U.S. Pat. No. 7,201,886 relates to a diamond tool comprising a shaped diamond and at least one layer of single crystal diamond doped with boron and/or isotopes of carbon to improve properties, including color, strength, electrical conductivity, and velocity of sound.
In contrast to CVD vapor doping process, boron-doped diamond crystals were manufactured by high pressure and high temperature (HP/HT) process in 1960's by a method of solid-state diffusion of boron atom into diamond using boron or boron compounds of B4C, B2O3, BN, NaB4O3, B10H14, NiB and LiBH4, as an activator at a pressure greater than 8.5 Gpa and a temperature greater 1300° C., disclosed in U.S. Pat. No. 3,141,855. Using a powder mixture of carbonaceous materials and boron or compounds containing boron such as B4C, B2O3, BN, B, NaB4O7, B10H14, NiB, LiBH4 and BP at a pressure great than 5 Gpa and a temperature greater than 1300° C., electrically conductive boron-doped diamond crystals were produced, disclosed in U.S. Pat. No. 3,148,161. However, high toughness of HP/HT doped diamond had not been reported at that time. Producing high quality doped-diamond crystals in the HP/HT process has proven to be expensive and difficult. U.S. Pat. No. 6,322,891 discloses heating a mixture of diamond, a source of boron and inert particles of alumina, magnesium oxide, or silicon oxide, at 800 to 1200° C. to facilitate solid-state diffusion of boron into the surface of diamond crystals and to form boron-doped diamond to improve oxidation and mechanical properties. Bovenkerk disclosed in U.S. Pat. No. 4,268,276 using HP/HT boron-doped diamond crystals to improve diamond-to-diamond self bond characteristics in 1981. No work has been directed to improve mechanical and wear properties of HP/HT polycrystalline boron-doped diamond compact.
More importantly, the solubility of born in diamond was observed to be as high as 7.9 wt %, that is ([B]=1.4×1022, where [B] is expressed in atoms/cm3) in the chemical vapor deposition process. In the past HP/HT processes, only a fraction of boron, about 300 ppm ([B]=3.3×1019) was incorporated into diamond crystals to form boron-doped diamond crystals. The present invention overcomes this limitation by using low-melting-temperature boron-containing Ni-alloys.